1) Field of the Invention
The present invention relates to a technique for transferring data between a plurality of logic devices provided in an external device, such as a disk drive unit, and an input/output request device (host) for making an input/output request to the plurality of logic devices, through use of a plurality of paths.
2) Description of the Related Art
FIG. 6 is a block diagram showing the configuration of a conventional data transfer system. As shown in FIG. 6, a conventional data transfer system 100 comprises a disk drive (external storage device) 105 having a plurality of logic devices (designated as “lun” in the drawings, where “lun” is an abbreviate of a logical number) 106a, 106b, and 106c; a host (input/output request device) 101 for making an input/output [hereinafter called an I/O (Input/Output)] request to the respective logic devices 106a to 106c of the disk drive unit 105; and a plurality of paths 108-1 to 108-4 which connect the host 101 to the disk drive 105 and which transfer data between the host 101 and the respective logic devices 106a to 106c of the disk drive 105.
The respective paths 108-1 to 108-4 are connected to host adapters (HBA: Host Bus Adapter) 104-1 to 104-4 of the host 101 as well as to channel adapters (CA: Channel Adapter) 107-1 to 107-4 of the disk drive 105 corresponding to the HBA 104-1 to 104-4, thereby connecting the host 101 to the disk drive 105.
The host 101 is provided with a computing section (e.g., a CPU: Central Processing Unit) 102, and further comprises a driver 103 which allocates, to the respective paths 108-1 to 108-4, I/O requests issued in accordance with an application program executed by the computing section 102.
At the time of allocating the I/O requests issued on the basis of the application executed by the computing section 102 of the host 101, such a conventional data transfer system 100 allocates the I/O requests such that the number of I/O requests in queues of the respective paths 108-1 to 108-4 or the quantity of data transferred becomes uniform among the paths 108-1 to 108-4, or allocates the I/O requests to the respective paths 108-1 to 108-4 on the basis of a preset load sharing.
However, if a change has arisen in the quantity of data flowing to the paths for reasons of a change in the operating state of the portion of the system ranging from the host 101 to the disk drive 105 or for reasons of transfer of data to a terminal other than the disk drive 105, processing capabilities of the respective paths 108-1 to 108-4 have become nonuniform. In the path whose processing capability has become deteriorated, access response to the I/O request is deteriorated, thereby causing a problem of a decrease in access speed.
There has already been proposed a technique for ascertaining loading conditions of the respective paths (i.e., the number of I/O requests or the quantity of data transferred) on the basis of the throughput of each path per unit time and varying proportions of the I/O requests distributed to the respective paths on the basis of the loading condition, thereby optimizing transfer efficiency (see Patent Document 1 provided below).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-320439
However, according to the data transfer system 100 shown in FIG. 6 and the technique disclosed in Patent Document 1, the respective logic devices 106a to 106c of the disk drive 105 are handled in a unified manner, thereby controlling a balance between the loads of the respective logic devices 106a to 106c. For this reason, the data retained in the respective logic devices 106a to 106c are also handled in a unified manner.
Consequently, the conventional data transfer system suffers the following problem. When an access speed is important in system operation; that is, when data for which required access response speed must be ensured and data for which access response speed is not required are coresident in the plurality of logic devices, an I/O request to data for which an access speed must be prioritized (i.e., an I/O request to a logic device retaining data for which an access speed must be prioritized) is hindered by an I/O request to another data set for which the access speed is not prioritized. As a result, the access response performance of the logic device retaining the data for which the access speed must be prioritized is deteriorated.